Gypsum board is one of the most widely used and versatile building materials in the world. The basic construction for gypsum building boards has remained unchanged for quite some time. This construction includes a core of calcium sulfate dihydrate (CaSO4 2H2O) that is sandwiched between opposing paper sheets.
The gypsum can be either artificially produced or mined. Naturally occurring gypsum must be ground and crushed in a mill prior to use. Thereafter the ground gypsum is heated in a kettle whereby it is calcined to produce calcium sulfate hemihydrate (CaSO4 ½H2O) (or stucco) in accordance with the following equation:CaSO42H2O+Heat→CaSO4½H2O+1½H2O
The calcined gypsum is thereafter mixed with water to form a stucco slurry. Other additives can be included such as accelerators, retarders, or starches. The slurry is advantageous because it allows the gypsum to be formed into any of a variety of shapes or sizes. In the manufacture of gypsum building boards, the slurry is poured out over a bottom sheet in a manufacturing line. A top sheet is then used to enclose the gypsum. The edges of the lower sheet can be turned up to form the edges of the wallboard. Further forming can take place via the use of rollers, guides, or hinge plates that are spaced out over a series of forming tables.
As the board passes over the forming tables, the water reacts with the stucco to reverse the above noted equation. As a result, the calcium sulfate hemihydrate (CaSO4 ½H2O) is converted to calcium sulfate dihydrate (CaSO4 2H2O) in accordance with the following equation:CaSO4½H2O+1½H2O→CaSO42H2O+Heat
After the gypsum completely sets, the boards are delivered to a gypsum board dryer where additional water vapor is driven out of the board. Finally, the boards are cut into desired lengths.
A significant problem has arisen regarding certain drywall that was imported into the United States from the People's Republic of China. Chinese drywall was imported into the United States during the housing boom starting around 2004. The gypsum used to produce this drywall had increased amounts of elemental sulfur. This elemental sulfur remained in the final gypsum wallboard. The suspicion was that the elemental sulfur produced sulfurous gas emissions, such as carbon disulfide, carbonyl sulfide, and hydrogen sulfide. Homeowners have reported that these emissions resulted in various household items becoming corroded. A litany of adverse health effects were also claimed as a result.
In response, the United States Congress passed the Drywall Safety Act of 2012 (DSA). The DSA was signed into law in 2013, Pub. L. No. 112-266, 126 Stat. 2437 (2013). The DSA directed the Consumer Products Safety Commission (CPSC) to promulgate a rule regarding acceptable levels of elemental sulfur in wallboard. In early 2015, the CPSC determined that ASTM C1396M-14a, “Standard Specification for Gypsum Board” was an acceptable standard that conformed to the requirements of the DSA and was consistent with elemental sulfur levels not associated with elevated rates of corrosion in the home. ASTM C1396M-14a was developed by Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products of ASTM International. The CPSC's determinations mean that the elemental sulfur content limit in ASTM C1396M-14a shall soon be treated as a consumer product safety rule promulgated under the Consumer Product Safety Act (CPSA). ASTM C1396M-14a states that Gypsum board shall contain not greater than 10 parts per million (PPM) of orthorhombic cyclooctasulfur (S8), when tested in accordance with Test Methods ASTM C471M.
The problems associated Chinese drywall have created a need to find ways to reduce or eliminate elemental sulfur from gypsum wall board. The present disclosure relates to methods of reducing elemental sulfur in gypsum via the addition of copper. The background art discloses various uses for copper in building materials.
For example, U.S. Pat. No. 8,926,855 to Thomas discloses building materials that include a dampening layer containing a plaster and a viscoelastic polymer. In certain embodiments, the dampening layer also includes a high atomic weight material, a high molecular density material, or a combination thereof. One example of such material is copper powder.
U.S. Pat. No. 6,676,744 to Merkley discloses fiber cement composite materials using cellulose fibers loaded with inorganic or organic substances. Copper is disclosed as one possible loading substance for the cellulose fibers.
U.S. Pub. App. 2015/0030532 to Sahin discloses an antimicrobial material comprising a metal ion charged with synthesized zeolite. Silver, zinc, and copper metal ion-charged zeolites can be used. The new construction materials are antimicrobial and prevent microorganism growth.
Although the above referenced inventions achieve their own individual objectives, none of the background art discloses reducing elemental sulfur in gypsum via the addition of copper.